1. Field of the Invention
The present invention relates to a photoelectric conversion device in which a crystalline silicon film is used and the fabrication method thereof.
2. Description of the Related Art
A photoelectric conversion device such as a solar cell has been well known as an attractive power generation means without carbon dioxide emissions. A photoelectric conversion device can be fabricated using a silicon semiconductor or a compound semiconductor, and a silicon semiconductor is used for most of photoelectric conversion devices sold in the market. A photoelectric conversion device in which a silicon semiconductor is used can be classified into a bulk photoelectric conversion device in which a wafer of single crystal silicon, polycrystalline silicon, or the like is used and a thin film photoelectric conversion device in which a silicon film is formed over a substrate. In order to spread photoelectric conversion devices, it is necessary to reduce the manufacturing cost. In the thin film photoelectric conversion device, the photoelectric conversion layer can be formed with a small amount of raw material in comparison with the bulk photoelectric conversion device; therefore, it is expected to reduce the cost.
Although, in the field of the thin film photoelectric conversion device, a photoelectric conversion device in which amorphous silicon is used is in practical use, its conversion efficiency is lower than that of a photoelectric conversion device in which single crystal silicon or polycrystalline silicon is used. In addition, the photoelectric conversion device in which amorphous silicon is used has problems specific to amorphous silicon such as a light deterioration phenomenon, and in some respects the device is not suitable to the outside use which requires large power generation. Therefore, a photoelectric conversion device including a crystal silicon thin film with high conversion efficiency and without a problem of light deterioration phenomenon has been developed.
The crystal silicon thin film can be formed by a vapor deposition method or a solid phase growth method. However, in the case where a glass substrate is used for a support body, it is difficult to achieve both a high growth speed capable of achieving the productivity and an excellent crystallinity even if either method is applied because the process temperature has an upper limitation.
As a method for solving the above problems, it is disclosed in Patent Document 1 that crystallization of an amorphous silicon film can be promoted by addition of a slight amount of a catalyst material. A heavy metal such as nickel (Ni), iron (Fe), cobalt (Co), or platinum (Pt) serves as a catalyst, and makes it possible to decrease the heat treatment temperature and to reduce the process time. Specifically, it is described in Patent Document 1 that a high-quality crystal can be obtained by a heat treatment performed at 550° C. for 4 hours.
In addition, a method for fabricating a thin film crystal silicon based photoelectric conversion device, in which gettering of a catalyst material is performed using phosphorus (P) or the like because the above heavy metal serves as a life time killer of carriers induced by light in a photoelectric conversion layer, is disclosed in Patent Document 2.